Docker

Docker Skill

Manage Docker containers and Compose stacks: build, run, stop, logs, exec, prune, multi-service orchestration.

Use When

• Building/running containers or debugging container issues
• Setting up docker-compose stacks
• Managing images, volumes, networks
• Containerizing applications
• Multi-service orchestration

Quick Reference

Container Lifecycle

# Run container (detached, with name, port mapping, env vars)
docker run -d --name myapp -p 8080:80 -e NODE_ENV=production --restart unless-stopped myimage:latest

# Interactive shell
docker exec -it myapp bash

# Logs (follow, with timestamps, last 100 lines)
docker logs -f --tail 100 --timestamps myapp

# Stop / remove
docker stop myapp && docker rm myapp

# List running (all with -a)
docker ps --format "table {{.Names}}\t{{.Status}}\t{{.Ports}}"

Building Images

# Build with tag
docker build -t myapp:latest .

# Multi-stage build (target specific stage)
docker build --target production -t myapp:prod .

# Build with build args
docker build --build-arg VERSION=1.2.3 -t myapp:1.2.3 .

# No cache rebuild
docker build --no-cache -t myapp:latest .

Docker Compose

# Start all services (detached)
docker compose up -d

# Start specific service
docker compose up -d postgres

# Rebuild and restart
docker compose up -d --build

# View logs across services
docker compose logs -f --tail 50

# Stop and remove everything (including volumes)
docker compose down -v

# Scale a service
docker compose up -d --scale worker=3

# Execute command in running service
docker compose exec web bash

# View service status
docker compose ps

Debugging

# Inspect container (full JSON)
docker inspect myapp

# Resource usage
docker stats --no-stream

# See container processes
docker top myapp

# Copy files out of container
docker cp myapp:/app/logs/error.log ./error.log

# Check why container exited
docker inspect --format='{{.State.ExitCode}} {{.State.Error}}' myapp

# Network debugging
docker network ls
docker network inspect bridge

# Enter stopped container's filesystem
docker run --rm -it --entrypoint sh myimage:latest

Cleanup

# Remove all stopped containers, unused networks, dangling images, build cache
docker system prune -f

# Also remove unused volumes (DESTRUCTIVE)
docker system prune -af --volumes

# Show disk usage
docker system df

# Remove dangling images only
docker image prune -f

# Remove images older than 24h
docker image prune -a --filter "until=24h"

Volumes & Networks

# Create named volume
docker volume create mydata

# Run with volume mount
docker run -d -v mydata:/app/data myapp

# Bind mount (host directory)
docker run -d -v $(pwd)/config:/app/config:ro myapp

# Create custom network
docker network create mynet
docker run -d --network mynet --name api myapi
docker run -d --network mynet --name web myweb  # can reach api by hostname

Helper Scripts

Generate docker-compose template

bash scripts/compose-gen.sh  [services...]
# Example: bash scripts/compose-gen.sh myproject web postgres redis

Check container health

bash scripts/health-check.sh [container-name|all]

Cleanup/prune with safety

bash scripts/cleanup.sh [--aggressive]

Common Patterns

Dockerfile — Node.js app

FROM node:20-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci --only=production
COPY . .
RUN npm run build

FROM node:20-alpine
WORKDIR /app
RUN addgroup -g 1001 appgroup && adduser -u 1001 -G appgroup -s /bin/sh -D appuser
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
COPY --from=builder /app/package.json ./
USER appuser
EXPOSE 3000
CMD ["node", "dist/index.js"]

Dockerfile — Python app

FROM python:3.12-slim
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
USER nobody
EXPOSE 8000
CMD ["gunicorn", "-w", "4", "-b", "0.0.0.0:8000", "app:app"]

Troubleshooting

| Problem | Solution | | -------------------------------- | ------------------------------------------------------ | | Container exits immediately | Check docker logs myapp, verify CMD/ENTRYPOINT | | Port already in use | lsof -i :8080 or change host port | | Permission denied on volume | Check UID mapping, use --user $(id -u):$(id -g) | | Can't connect between containers | Use same network, reference by container name | | Out of disk space | docker system prune -af --volumes | | Build cache too large | docker builder prune -af | | DNS issues in container | docker run --dns 8.8.8.8 or check /etc/resolv.conf |

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: JansenAnalytics
• Source: JansenAnalytics/claudex
• License: MIT

Install and usage instructions live in the source repository linked above.